Heat treatment of aluminum castings



d The invention relates to the heat treatment Patented May 14, 1929 UNITED STATES- PATENT OFF-ICE.

RANDOLPH J. ROSHIRT, OF DET'IROI'I', MICHIGAN, ASSIGIN'OR TO BOHN ALUMINUM & BRASS CORPORATION, 015 DETROIT, MICHIGAN; A CORPORATION OF MICHIGAN.

HEAT TREATMENT OF ALUMINUM CASTINGS.

Ho Drawing.

. of aluminum alloy castings and is particu- 'larly applicable to the treatment of the metalcast pistons: The primary object of'the invention is to improve the physical characteristics of the alloy particularly to increase the hardness and to refine the grain, thereby increasing the resistance of the piston to scoring.

One of the common aluminum alloys used for piston castings contains approximately 10% copper, 1% iron, 0.5% magnesium and the balance principally aluminum, although sometimes nickel and other elements are introduced under certain conditions. This aluminum alloy when cast in metal molds has a hardness ranging from 90 to 110 Brinell.

My invention consists in providing a heat treatment for the cast alloy adaptable for use on a commercial scale, whereby the pistons may be increased in hardness, and held to a minimum Brinell of 130 or 140 as desired. It will of course be understood that in establishing a minimum Brinell limit, the average hardness of a series of heat treated pistons V will be above this limit. Therefore the heat treatment to obtain a minimum of 130 gen-' erally results in a range or hardness from 130 to 150, while the treatment to obtain 140 minimum results in a range from 140 to 160.

My heat treatment is carried out in two steps, first by heating the castings to a temperature as high as possible without causing distortion and uenching in water from this heat. Second y subjecting the quenched pistons to a lower temperature for a longer period of time and then air cooling. In carrying out the first ste the pistons are heated to a temperature o from 925 to 975 F. and held at heat for approximately two hours, after which they are quenched in cold water. The preferred temperature is 950 F. This step in itself increases the hardness of the castings for when measured after aging at ordinary room temperatures, the Brinell readings range from 100 to 120.

The second step further increases the hardness of the castings, but there are two factors which must be carefully selected to obtain the maximum from the alloy, these being the temperature and the time at heat. ,I have found that the best temperature for securing maximum hardness is from 425 to 475. F., preferably held as close as possible to 450 F. The

Application filed January 18, 1928. Serial R'o. 82,132.

time which the castings are held at this temperature may be varied according to the hard- While I have specifically described above the heat treating of aluminum alloy pistons, I wish it understood that the treatment is also applicable to 'other aluminum alloy castings and may be used to obtain a product having greater minimum hardness than any heretofore produced by commercial methods.

W at I claim as my invention is:

1. The process of heat treating aluminum alloys, comprising heating the alloy to a temperature as high as possible without distortion of the same, quenching from said heat and reheating at a temperature from 425 to 475 F.

2. The process of heat treating aluminum alloy castings, comprising heating the casting to a temperature'of from 925 to 975 F., quenching the casting from said heat and reheating at a temperature of from 425 to 475 F.

1 3. The process of heattreating aluminum alloy castings, comprising heating the castings to a temperature of approximately 950 F. and reheating to a temperature of approximately 450 F. for six hours or over.

4. The process of manufacturing istons, comprising the casting of a piston blank in a metal mold from an alloy containing 10% copper, 1% iron and, 0.5%.magnesium, the balance being princi ally aluminum, heating said casting blan to a temperature of approximately 950 F., quenching and reheating at a temperature of approximately 450 F. for six hours or over.

- 5. An unworked cast aluminum base alloy containin approximately 10% cop er, 1% iron an 0.5% magnesium, the aloy having been quenched at a temperature .said alloy having Brinell hardness of 130 or over.

7. The process of manufacturing aluminum alloy products comprising the casting of the product in a metal mold from an alloy containing 10% copper, 1% iron and 0.5% magnesium and the balance principally aluminum, heating the unworked casting to a temperature of-925 to 975 F., uenching and reheating at a temperature of irom 425 to 475 F. for not less than six hours to obtain a Brinell hardness of'130 or over.

8. The process of manufacturing aluminum alloy products comprising the casting of the product in a metal mold from an alloy containing 10% copper, 1% iron and 0.5% magnesium and the balance principally aluminum, heating the unworked casting to a temperature of 925 to 975 F., Quenching and reheating at a temperature of rom 425 to 475 F. for at least six hours and not over twelve hours to obtain -a Brinell hardness of 130 or over.

9. The rocess of heat treating aluminum alloy castings, comprising heating the cast ings to a temperature of approximately 950 F., and reheating to a temperature of approximately 450 F.

10. The process of manufacturing pistons, comprising the casting of a piston blank in a metal mold from an alloy containing approximately 10% copper, 1% iron and 0.5% magnesium, the balance being rincipally aluminum, heating said casting lilank to a temperature of approximately 950 F., quenching and reheating at a temperature of approximately 450 F.

11. An unworked cast aluminum base a1- loy containing approximately 10% copper, 1% iron and 0.5% magnesium, the alloy having been quenched at a temperature above 925 F., and reheated at a temperature above 425 F., said alloy having Brinell hardness of 130 or over.

12. The process of manufacturing aluminum alloy products comprisin the casting of the product in a metal mold roin an alloy containing aproximately 10% copper, 1% iron and 0.5%- magnesium and the balance principally aluminum, heating the unworked casting to a temperature of 925 to 975 F., quenching and reheating-at a temperature of from 425 to 475 F. to obtain a Brinell hardness of 130 or over.

13. An unworked cast aluminum base al- 10y having a Brinell hardness of 130 or over, said alloy having been quenched at, a term perature above 925 F. and reheated at a temperature above 425 F.

In testimony whereof I afiix my signature.

RANDOLPH J. ROSHIRT. 

